Wandering Investor

It is difficult for Cognitive Shadows to ascend to shards at all. Kelsier only managed to do so thanks to the IRE's device. Not to mention, by the time Vin or Ati had collected their wits, Sazed already had the shards.
As for a hypothetical scenario in which Ruin was killed and his cognitive shadow was allowed the chance to take up Ruin again, I don't think it would work. Its debatable whether most cognitive shadows have souls, and even if they did they wouldn't have a physical aspect. That would make it difficult to ascend and control the shard. 

Oh, so you're talking about putting a physical object into either the spiritual realm or cognitive realm, and then retrieving for later use? I'm not aware of any that work with the spiritual realm, although if that were the case, that'd be your best bet. And for the cognitive, you'd have to be able to create perpendicularity, which require a lot of power. Your Elsecallers and and Willshapers may be able to do so, which large amounts of investiture required. Assuming no one messed with the object while it was in the cognitive. But if you're looking for storing it in a magical pocket dimension.. no.